Wafer level stacked structures having integrated passive features

ABSTRACT

A method includes obtaining an active feature layer having a first surface bearing one or more active feature areas. A first capacitor plate of a first capacitor is formed on an interior surface of a cap. A second capacitor plate of the first capacitor is formed on an exterior surface of the cap. The first capacitor plate of the first capacitor overlays and is spaced apart from the second capacitor plate of the first capacitor along a direction that is orthogonal to the exterior surface of the cap to form the first capacitor. The cap is coupled with the first surface of the active feature layer such that the second capacitor plate of the first capacitor is in electrical communication with at least a first active feature of the active feature layer. The cap is bonded with the passive layer substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.16/666,016, filed Oct. 28, 2019, and entitled “WAFER LEVEL STACKEDSTRUCTURES HAVING INTEGRATED PASSIVE FEATURES,” the contents anddisclosures of which are hereby incorporated by reference in theirentirety.

BACKGROUND

MEMS features may include electromechanical MEMS features (e.g.,switches, piezoelectric devices, and the like) and/or passive MEMSfeatures (e.g., capacitors, resistors, inductors, and the like). Forexample, an RF module for a wireless device may employ tens of MEMSswitches to facilitate receiving, processing, and transmitting signalsand tens of MEMS capacitors to provide, e.g., direct current (DC)isolation on transmission lines and the like, to the resultant devices.Conventionally, device layers bearing passive MEMS features are formedseparately from active feature layers bearing active features (e.g.,sources, gates, drains, capacitors, resistors, and the like) andelectromechanical MEMS feature layers bearing electromechanical MEMSfeatures. The passive MEMS features are subsequently placed inconductive communication with at least the active features and coupledto the active feature layer and/or an intermediate layer such as anelectromechanical MEMS feature layer.

Passive MEMS features may be formed directly on the cap layer of theradio frequency (RF) MEMS device or an intermediate layer (e.g., anelectromechanical MEMS feature layer, and the like). There are numerouslimitations and challenges associated with forming passive MEMS featuresdirectly on cap layers and/or on intermediate layers. Passive MEMSfeatures are conventionally formed in fabrication processes that areadjunct to the processes used to form active feature layers andintermediate layers of RF MEMS devices (e.g., an RF MEMS switch). Forexample, passive MEMS features may be formed on portions of the activefeature layer or an intermediate layer. In a further example, passiveMEMS features may be formed directly on portions of the cap layer orintermediate layer using a metal/metal oxide/insulator-based process toform, e.g., a free-standing capacitor. Such a fabrication process mayadd significant time (e.g., days or weeks) and cost to the final RF MEMSdevice. Furthermore, passive MEMS features (e.g., capacitors) formed bysuch processes may suffer from edge effects impacting the maximumallowable voltage, inherent leakage, and asymmetric leakage with thepolarity of voltage applied to the capacitor. Accordingly, RF MEMSdevices and systems would benefit from a lower-cost andhigher-performance approaches to packaging and integration.

BREIF DESCRIPTION

In one embodiment, a method includes obtaining an active feature layer.The active feature layer has a first surface bearing one or more activefeature areas and a cap disposed on the active feature layer over theone or more active feature areas. A first electrical connection isformed in electrical communication with a first active feature through afirst contact pad disposed on an interior surface of the cap. A firstcapacitor plate of a first capacitor is formed on an exterior surface ofthe cap in electrical communication with the electrical connection. Afirst bonding pad is formed at a different, spaced-apart location fromthe first capacitor plate on the exterior surface of the cap. A secondcapacitor plate of the first capacitor is formed on an interior surfaceof a passive layer substrate. The passive layer substrate includes atleast one of a silicon-based ceramic, an aluminum-based ceramic, or atantalum-based ceramic. The cap is coupled with the passive layersubstrate so that a first area of the first bonding pad on the capcontacts the second capacitor plate of the first capacitor on thepassive layer substrate and a different, second area of the secondcapacitor plate of the first capacitor overlays and is spaced apart fromthe first capacitor plate of the first capacitor along a direction thatis orthogonal to the exterior surface of the cap to form the firstcapacitor. The cap is bonded with the passive layer substrate.

In one embodiment, a method includes obtaining an active feature layerhaving a first surface bearing one or more active feature areas. A firstcapacitor plate of a first capacitor is formed on an interior surface ofa cap. A second capacitor plate of the first capacitor is formed on anexterior surface of the cap. The first capacitor plate of the firstcapacitor overlays and is spaced apart from the second capacitor plateof the first capacitor along a direction that is orthogonal to theexterior surface of the cap to form the first capacitor. The cap iscoupled with the first surface of the active feature layer such that thesecond capacitor plate of the first capacitor is in electricalcommunication with at least a first active feature of the active featurelayer. The cap is bonded with the passive layer substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The present inventive subject matter will be better understood fromreading the following description of non-limiting embodiments, withreference to the attached drawings.

FIG. 1 illustrates a schematic partial cross-sectional view of anexample RF MEMS device including integrated passive features inaccordance with embodiments herein.

FIG. 2 is a flowchart describing an example process for fabricating theRF MEMS device of FIG. 1 in accordance with embodiments herein.

FIG. 3A-3E are schematic, partial cross-sectional views illustrating thefabrication steps of the process of FIG. 2 in accordance withembodiments herein.

FIG. 4 illustrates a schematic partial cross-sectional view of anexample RF MEMS device including integrated passive features inaccordance with embodiments herein.

FIG. 5 is a flowchart describing an example process for fabricating theRF MEMS device of FIG. 4 in accordance with embodiments herein.

FIG. 6A-6G are schematic, partial cross-sectional views illustrating thefabrication steps of the process of FIG. 5 in accordance withembodiments herein.

DETAILED DESCRIPTION

The following detailed description illustrates the inventive subjectmatter by way of example and not by way of limitation. The descriptionenables one of ordinary skill in the art to make and use the inventivesubject matter, describes several embodiments of the inventive subjectmatter, as well as adaptations, variations, alternatives, and uses ofthe inventive subject matter. Additionally, it is to be understood thatthe inventive subject matter is not limited in its application to thedetails of construction and the arrangements of components set forth inthe following description or illustrated in the drawings. The inventivesubject matter is capable of other embodiments and of being practiced orbeing carried out in various ways. Also, it is to be understood that thephraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting on all embodiments ofthe inventive subject matter.

The inventive subject matter described herein provides methods forforming wafer level stacked MEMS devices having integrated passivefeatures (e.g., capacitors, inductors, and the like), along with devicesformed thereby. Such methods and devices can enable the creation ofhigher performance RF circuits by integrating the passive MEMS featuresinto a bonded wafer pair structure formed at least in part by a portionof an intermediate layer (e.g., an electromechanical MEMS feature layer,a cap, and the like). Such methods can reduce the time and cost tofabricate RF MEMS devices that include active features, passive MEMSfeatures, and optionally, electromechanical MEMS features. Such methodsalso may reduce the size of the RF MEMS devices as compared toconventional RF MEMS devices. RF MEMS devices formed by the presentmethods may also exhibit improved performance compared to conventionalRF MEMS devices due to one or more of reduced leakage current, increasedvoltage capability, athermal performance, and the like. For the sake ofclarity, the specific example of an RF MEMS switch is discussed;however, the present methods can be applied to many different types ofRF MEMS devices that utilize passive features. For example, the presentmethods may be utilized to fabricate RF MEMS devices and/or modules forselectively coupling and/or decoupling one or more inductors of aninductor system, such RF MEMS devices and/or modules being implementedin a magnetic resonance imaging (MRI) system, a radar system, and thelike.

FIG. 1 illustrates a schematic partial cross-sectional view of anexample RF MEMS device 100 including integrated passive features inaccordance with embodiments herein. The RF MEMS device 100 includes, asactive features, a source 102, a drain 104, and a gate 108 formed onand/or in the active feature substrate (or layer) 112. The source 102and the drain 104 are selectively placed in conductive communication andpass electrical signals upon actuation of a switch 106. The switch 106is one example of an electromechanical MEMS feature. The switch 106 iscantilevered and includes a beam portion 116 having a contact portion118 disposed on a lower surface of a first end thereof for contactingthe drain 104 and an anchor portion 120 on a second end opposite thefirst end. The anchor portion 120 is in electrical communication withthe source 102. The switch 106 actuates so the contact portion 118 is inelectrical communication with the drain 104 when a sufficientelectrostatic force is applied to the switch 106 based on an actuationvoltage applied at a gate 108. The actuation voltage is applied to thegate 108 through a gate line 110 in electrical communication with anelectrical feedthrough 114 (e.g., a blind via). The electricalconnection 114 (e.g., a feedthrough or the like) is in electricalcommunication with a voltage source (not shown) applied to a contact pad(not shown) on an exterior of the RF MEMS device 100 through conductivetrace 115. When the contact portion 118 of the switch 106 contacts thedrain 104, electrical signals are transmitted along a signaltransmission line that includes at least the source 102 and the drain104. (The example switch 106 is configured in a normally off positionfor the sake of clarity; however, switches biased to a normally onposition are encompassed by the inventive subject matter describedherein.)

The switch 106 is surrounded by a cavity 126 (e.g., an air cavity, gascavity, or the like) formed by a barrier or cap 128 imposed on portionsof the surface of the active feature layer at a peripheral regionsurrounding one or more electromechanical MEMS features (e.g., one ormore switches 106) and active features (e.g., source 102, drain 104, andgate 108). The cap 128 includes an interior surface 130 and an opposedexterior surface 132. The cap 128 comprises an insulating substrate(e.g., silicon-based ceramic, an aluminum-based ceramic, or atantalum-based ceramic, glass, fused silica, and the like) having gooddielectric properties. The cap 128 may be bonded to the active featuresubstrate 112 at a peripheral region using at least one of metalthermocompression bonding, eutectic bonding, anodic bonding, localizeddirect laser bonding, or glass frit bonding of the cap to the passivesubstrate. In one example, the cap 128 is bonded to the active featuresubstrate 112 using Au-Au compression bonding. The cap 128 providesmechanical, electrical, chemical, and/or environmental protection forthe underlaying active, passive, and/or electromechanical MEMS features.

The RF MEMS device 100 also includes, as passive MEMS features, a firstcapacitor 122 capacitively coupled with the source 102 and a secondcapacitor 124 capacitively coupled with the drain 104. In the example ofFIG. 1 , the first capacitor 122 includes a first capacitor plate 122 adisposed on the interior surface 130 of the cap 128 in electricalcommunication with the source 102 and a second capacitor plate 122 bdisposed on the exterior surface 132 of the cap 128. The first capacitorplate 122 a and the second capacitor plate 122 b are aligned to overlayeach other and spaced apart by the intervening portion of the cap 128.The intervening portion of the cap 128 establishes the gap for the firstcapacitor 122. The intervening portion of the cap 128 may also have areduced height (H_(r)) compared to the height (H_(n))of the portions ofthe cap 128 adjacent the intervening portion in order to tailor thecapacitance of the first capacitor 122. For example, a cap having a 300μm nominal height adjacent the intervening portion of the cap 128 can beetched on the interior surface 130 to reduce the height of theintervening portion of the cap 128 to 100 μm to create a partial via134.

The second capacitor 124 includes a first capacitor plate 124 a disposedon the interior surface 130 of the cap 128 in electrical communicationwith the drain 104 and a second capacitor plate 124 b disposed on theexterior surface 132 of the cap 128 and is substantially similar to thefirst capacitor 124. As used herein, “substantially similar” indicatesthat the second capacitor 124 bears at least about 90% or more of thetraits of the first capacitor 122.

The RF MEMS device 100 is configured to capacitively couple electricalsignals to the source 102 through the first capacitor 122 andcapacitively couple electrical signals out of the drain 104 through thesecond capacitor 124 of the RF MEMS device 100, eliminating directelectrical connections between the capacitors 122, 124 and thecorresponding source 102 and drain 104.

The RF MEMS device 100 may also be hermetically sealed. The term“hermetic” refers to a bond or seal whose quality (e.g., leak rate) isdefined in units of atm-cc/sec, which is the amount of gas (in cc) thatis transferred into the package under an ambient atmospheric pressure ora range of ambient atmospheric pressures. For example, the passive MEMSlayer (e.g., the bonded active substrate, cap, and, optionally, passivesubstrates housing the passive MEMS features) disclosed herein iscapable of providing a hermetic seal having a leak rate no greater thanabout 5×10{circumflex over ( )}8 atm cc/s air equivalent leak rate, andmay exhibit a leak rate no higher than about 1×10{circumflex over ( )}6atm cc/sec air equivalent. Additionally or alternatively, the activefeature layer disclosed herein is capable of providing a hermetic seal,with respect to the active features housed in the active feature layer,having a leak rate no greater than about 5×10{circumflex over ( )}8 atmcc/s air equivalent , and may exhibit a leak rate no higher than about1×10{circumflex over ( )}6 atm cc/sec air equivalent. It is alsoconsidered that performance of a successful hermetic seal is to bejudged by the user, designer or manufacturer as appropriate, and that“hermetic” ultimately implies a standard that is to be defined by auser, designer, manufacturer or other interested party.

The active features (e.g., the source 102, the drain 104, the gate 108,the gate line 110, and the like) are formed in and/or on the activefeature substrate 112 and, together, comprise an active feature layer.In the instant disclosure, when features and/or layers are beingdescribed as “on” or “over” another feature, layer, or substrate, it isto be understood that the features, layers, and/or substrates can eitherbe directly contacting each other in one embodiment or have anotherlayer or feature between the layers in another embodiment, unlessexpressly stated to the contrary. Thus, these terms are simplydescribing the relative position of the features, layers, and/orsubstrates to each other and do not necessarily mean “on top of” sincethe relative position above or below depends upon the orientation of thedevice to the viewer. Additionally, the active feature layer may includevarious other substrates, active features, contacts for these features,and interconnects between these features. The active feature layer maybe formed using semiconductor, CMOS (complementary metaloxide-semiconductor), and MEMS fabrication techniques.

The active feature layer may be made of materials appropriate for aparticular active feature or system. Example materials used to formactive feature layers include, but are not limited to, silicon (Si), Sicompounds, germanium, germanium (Ge) compounds, gallium (Ga), Gacompounds, indium (In), In compounds, or other semiconductor materialsand/or compounds. In addition, the active feature layer can includenon-semiconductor substrate materials, including any dielectricmaterials, metals (e.g., titanium, gold, copper, and aluminum), orceramics or organic materials found in printed wiring boards, forexample. In an example, the active feature layer may be formed on asilicon carbide (SiC) or a gallium nitride (GaN) substrate. Materials,such as semiconductors, metals and metal alloys, are discussed in theinstant disclosure using their common chemical abbreviation, such ascommonly found on a periodic table of elements. For example, tantalum isrepresented by its common chemical abbreviation Ta, tantalum oxide isrepresented by its common chemical abbreviation TaO, and so forth.

The electromechanical MEMS feature layer includes the switch 106. Theswitch 106 may be formed directly on portions of the active featurelayer. Additionally or alternatively, the electromechanical MEMS featurelayer may include an intermediate layer (e.g., the cap 128) andelectromechanical MEMS features (e.g., the switch 106) may be at leastpartially formed on the intermediate layer. The intermediate layerand/or the cap 128 may comprise an insulating substrate (e.g.,silicon-based ceramic, an aluminum-based ceramic, or a tantalum-basedceramic, glass, fused silica, and the like) having good dielectricproperties.

The connection 114, conductive trace 115, and the contact pad (notshown) on an exterior of the RF MEMS device 100 are formed fromconductors such as metals and/or metal alloys, subject to appropriateconsiderations such as adhesion and thermal properties.

In accordance with one embodiment, a process for forming RF MEMS deviceshaving integrated passive features is described in connection with FIG.2 and FIGS. 3A-3E. It should be noted that for clarity, some portions ofthe fabrication process of the RF MEMS devices 100 are not included inFIG. 2 and only the portions of the device package proximate one activefeature area (e.g., including one source 102, drain 104, and gate 108)of the active feature layer are illustrated in FIGS. 3A-3E. As such, thefollowing fabrication process is not intended to be an exhaustive listthat includes all steps required for fabricating the device package 100.In addition, the fabrication process is flexible because the processsteps may be performed in a different order than the order illustratedin FIG. 2 or some steps may be performed simultaneously.

Referring now to FIGS. 2 and 3A, at 202, an active feature layer 302 isobtained. The active feature layer 302 includes active features (e.g.,the source 102, the drain 104, the gate 108, the gate line 110, and thelike) formed in and/or on the active feature substrate 112. (The activefeature substrate/layer 302, 602 may also include capacitors andresistors, with or without additional active features.) The activefeature layer may include various other active components, contacts forthese components, and interconnects between these components. The activefeature layer 302 has a first surface with one or more active featureareas 303. In one example, the active feature area 303 may include athree terminal active feature formed by the source 102, the drain 104,the gate 108, the gate line 110, and, optionally any additionalconductive and/or metal features associated with the terminals.

At 204, the electromechanical MEMS feature layer is formed on the activefeature layer. For example, the switch 106 may be formed directly onportions of the active feature layer 302 using techniques such as, forexample and without limitation, suitable patterning, etching,anodization, electroplating, and deposition (e.g., chemical vapordeposition and/or physical vapor deposition) techniques. The switch 106includes a beam portion 116 having a contact portion 118 disposed on alower surface of a first end thereof and an anchor portion 120 on asecond end opposite the first end, the anchor portion 120 in electricalcommunication with the source 102. The switch 106 may be formed from oneor more different metals, such as gold, gold alloy, nickel, nickelalloy, tungsten, or the like. For example, the anchor portion 120 andthe beam 116 may be formed by depositing a suitable seed layer on aportion of the source 102 (e.g., the source electrode itself or aconductive trace extending from the source electrode) and depositing asuitable metal on top of the seed layer. In an additional or alternativeexample, the contact 118 may be formed from a different type of metal ormetal alloy than the beam 116 using, optionally, a suitable adhesionlayer. The result of operation 204 is illustrated in FIG. 3B.

At 206, a cap 128 is obtained and, at 208, a recess corresponding to thecavity 126 and, optionally, partial vias 134 corresponding to one ormore of the first and second capacitors 122, 124 and a through via 306corresponding to the electrical connection 114 (e.g., a feedthrough, ablind via, or the like) are formed in the interior surface 130 of thecap 128. For example and without limitation, suitable patterning andetching techniques are used to create the recess corresponding to thecavity 126 and, optionally, partial vias 134 corresponding to one ormore of the first and second capacitors 122, 124. The result ofoperation 208 is illustrated in FIG. 3C.

At 210, the first capacitor plates 122 a, 124 a, along with additionalconductive and/or metal features to establish electrical communicationbetween the various active, electromechanical, and passive features ofthe RF MEMS device 100 and, optionally, to bond the cap 128 to theactive feature layer, are formed on the interior surface 130 of the cap128. For example, the first capacitor plates 122 a, 124 a, along withany additional conductive and/or metal features, are formed on the cap128 using techniques such as, for example and without limitation,suitable patterning, etching, anodization, electroplating, anddeposition (e.g., chemical vapor deposition and/or physical vapordeposition) techniques. The result of operation 210 is illustrated inFIG. 3D.

At 212, the second capacitor plates 122 b, 124 b, along with additionalconductive and/or metal features (e.g., electrical connection 114 andconductive trace 115) to establish electrical communication between thevarious active, electromechanical, and passive features of the RF MEMSdevice 100, are formed on the exterior surface 132 of the cap 128.During formation, at least the second capacitor plates 122 b, 124 b arealigned with the first capacitor plates 122 a, 124 a using, e.g., astepper, to ensure a high degree of geometric control and precisealignment between the first capacitor plates 122 a, 124 a and the secondcapacitor plates 122 b, 124 b, and, optionally, between any additionalconductive and/or metal features. For example, the second capacitorplates 122 b, 124 b, along with any additional conductive and/or metalfeatures, are formed on the exterior surface 132 of the cap 128 usingtechniques such as, for example and without limitation suitablepatterning, etching, anodization, electroplating, and deposition (e.g.,chemical vapor deposition and/or physical vapor deposition) techniques.The result of operation 212 is illustrated in FIG. 3E.

At 214, the interior surface 130 of the cap 128 is aligned with, imposedon, and bonded to the surface of the active feature layer bearing activefeatures. For example, the recess corresponding to the cavity 126 isaligned with the switch 106, the first capacitor is aligned with and inelectrical communication with the source 102, the second capacitor isaligned with and in electrical communication with the drain 104, and thegate line is aligned with and in electrical communication with aconductive contact 117 on the interior surface 130 of the cap 128. Inone example, the cap 128 and the active feature layer are bonded using,e.g., an Au-Au compression bond. In an additional or alternativeexample, the cap 128 and the active feature layer are hermeticallybonded. The result of operation 214 is illustrated in FIG. 1 .Accordingly, the RF MEMS device 100 provides improved electrical,mechanical, and environmental isolation.

FIG. 4 illustrates a schematic partial cross-sectional view of anexample RF MEMS device 400 including integrated passive features inaccordance with embodiments herein. The RF MEMS device 400 includes manycommon active features and electromechanical MEMS features as the RFMEMS device 100 of FIG. 1 (as indicated by the common referencenumbers), but differs with regard to the configuration of the integratedpassive features. The RF MEMS device 400 includes a first capacitor 422that is in electrical communication with the source 102 throughelectrical connection 414 (e.g., a feedthrough or the like) and a secondcapacitor 424 that is in electrical communication with the drain 104through electrical connection 416. The RF MEMS device 400 is configuredto conduct electrical signals and/or energy to the source 102 throughthe first capacitor 422 and conduct electrical signals and/or energy outof the drain 104 through the second capacitor 424.

In the example of FIG. 4 , the first capacitor 422 includes a firstcapacitor plate 422 a disposed on the exterior surface 132 of the cap128 for the active feature layer. The first capacitor plate 422 a is inelectrical communication with the source 102 through the electricalconnection 414 (e.g., a feedthrough, a blind via, or the like) thatextends through the cap 128 to an electrical contact 412 disposed on theinterior surface 130 of the cap 128. The first capacitor 422 includes asecond capacitor plate 422 b disposed on an interior surface 418 of apassive substrate 420 for the passive MEMS feature layer. The firstcapacitor plate 422 a and the second capacitor plate 422 b are disposedin a first recess 430 between the cap 128 and the passive substrate 420.The first capacitor plate 422 a and the second capacitor plate 422 b arealigned to overlay each other and are spaced apart by a gap normal tothe first capacitor plate 422 a.

Likewise, the second capacitor 424 includes a first capacitor plate 424a disposed on the exterior surface 132 of the cap 128 for the activefeature layer. The first capacitor plate 424 a is in electricalcommunication with the source 102 through electrical connection 416(e.g., a feedthrough, a blind via, or the like) extending through thecap 128 and the electrical contact 410 disposed on the interior surface130 of the cap 128. The second capacitor 424 includes a second capacitorplate 424 b disposed on the interior surface 418 of the passivesubstrate 420 for the passive MEMS feature layer. The first capacitorplate 424 a and the second capacitor plate 424 b are disposed in asecond recess 432 between the cap 128 and the passive substrate 420. Thefirst capacitor plate 424 a and the second capacitor plate 424 b arealigned to overlay each other and are spaced apart by a gap normal tothe first capacitor plate 424 a.

The cap 128 and the passive substrate 420 each comprise an insulatingsubstrate (e.g., silicon-based ceramic, an aluminum-based ceramic, or atantalum-based ceramic, glass, fused silica, and the like) having gooddielectric properties. The cap 128 and the passive substrate 420 eachprovide mechanical, electrical, chemical, and/or environmentalprotection for the underlaying active, passive, and/or electromechanicalMEMS features. The cap and the passive substrate may be bonded using,for example and without limitation, metal thermocompression bonding,eutectic bonding, anodic bonding, localized direct laser bonding, orglass frit bonding of the cap to the passive substrate. In one example,the cap and passive substrate are bonded using Au-Au compressionbonding. The RF MEMS device 400 may also be hermetically sealed betweenthe cap and the active feature layer and/or the cap and the passivesubstrate.

Optionally, one or more of the first capacitor 422 and the secondcapacitor 424 are configured to exhibit athermal performance. The term“athermal performance” refers to the stability of a device (e.g., apassive MEMS device) over a range of operating temperatures. In anexample, the first and second capacitors 422, 424 may be formed bybalancing the height of the first capacitor plates 422 a, 424 a, thesecond capacitor plates 422 b, 424 b, and adjacent features (e.g.,bonding pads 426, 428) on opposing sides of the respective cavity 430,432 to cancel out coefficient of thermal expansion (CTE) effects over aselect range of temperatures (e.g. a range of operating temperatures).In an additional or alternative example, the height of the firstcapacitor plates 422 a, 424 a, the second capacitor plates 422 b, 424 b,and adjacent features (e.g., bonding pads 426, 428) are formed to have acommon height (normal to the first capacitor plate 422 a, 424 a) and thefirst capacitor plates 422 a, 424 a are disposed in a recess 434, 436formed in the cap. The depth of the recess 434, 436 normal to the firstcapacitor plates 422 a, 424 a is greater than the common height andestablishes the gap between the first capacitor plates 422 a, 424 a andthe second capacitor plates 422 b, 424 b. Over a range of operatingtemperatures, the first capacitor plates 422 a, 424 a, the secondcapacitor plates 422 b, 424 b, and adjacent features (e.g., bonding pads426, 428), may exhibit a change in height due to the CTE of the materialforming said features. Due to the common height, the changes in heightfor each of the first capacitor plates 422 a, 424 a, the secondcapacitor plates 422 b, 424 b, and adjacent features (e.g., bonding pads426, 428) for one or more of the capacitors 422, 424 will be the same.Accordingly, the air gap for the capacitors 422, 424 will remain thesame over the range of operating temperatures regardless of CTE effects,ensuring athermal performance of the capacitors 422, 424.

In accordance with one embodiment of the inventive subject matterdescribed herein, an example process for forming RF MEMS devices havingintegrated passive features is discussed in regard to FIG. 5 and FIGS.6A-6G. It should be noted that for clarity, some portions of thefabrication process of the RF MEMS device 400 are not included in FIG. 5and only the portions of the device package proximate one active featurearea (e.g., including one source 102, drain 104, and gate 108) of theactive feature layer are illustrated in FIGS. 6A-6G. As such, thefollowing fabrication process is not intended to be an exhaustive listthat includes all steps required for fabricating the device package 400.In addition, the fabrication process is flexible because the processsteps may be performed in a different order than the order illustratedin FIG. 5 or some steps may be performed simultaneously.

Referring now to FIGS. 5 and 6A, at 502, an active feature layer 602 isobtained, as described above.

At 504, the electromechanical MEMS feature layer is formed on the activefeature layer as described above. The result of 504 is illustrated inFIG. 6B.

At 506, the cap 128 for the active feature layer is obtained and, at508, the recess corresponding to the cavity 126, through vias 604, 606corresponding to the first and second electrical connections 414, 416(e.g., feedthroughs or the like), and a through via 608 corresponding tothe electrical connection 114 (e.g., a feedthrough, a blind via, or thelike) are formed in the interior surface 130 or through the height ofthe cap 128 as appropriate. Optionally, recesses 434, 436 correspondingto one or more of the first capacitor plates 422 a, 424 a are formed inthe exterior surface 132 of the cap. For example, suitable patterningand etching techniques are used to create the recess corresponding tothe cavity 126, the through vias corresponding to electrical connections114, 414, 416, and, optionally, the recesses 434, 436 corresponding toone or more of the first and second capacitor plates 422 a, 424 a. Theresult of operation 508 is illustrated in FIG. 6C.

At 510, the first capacitor plates 422 a, 424 a, the electrical contacts410, 412, the electrical connections 114, 414, 416, (e.g., feedthroughs,blind vias, or the like) along with additional conductive and/or metalfeatures to establish electrical communication between the variousactive, electromechanical, and passive features of the RF MEMS device400 and, optionally, to bond the cap 128 to one or more of the activefeature layer and the passive substrate 420, are formed on the interiorsurface 130 and the exterior surface 132 of the cap 128, as appropriate.For example, the first capacitor plates 422 a, 424 a, the electricalcontacts 410, 412, the electrical connections 114, 414, 416, along withadditional conductive and/or metal features, are formed on the cap 128using techniques such as, for example and without limitation, suitablepatterning, etching, anodization, electroplating, and deposition (e.g.,chemical vapor deposition and/or physical vapor deposition) techniques.The passive substrate 420 may have the at least one of the silicon-basedceramic, aluminum-based ceramic, or tantalum-based ceramic formed withinthe passive substrate 420. The result of operation 510 is illustrated inFIG. 6D.

At 512, the passive substrate 420 is obtained and, at 514, optionally,recesses 610, 612 corresponding to one or more of the second capacitorplates 422 b, 424 b are formed in the interior surface 418 of the cap.For example and without limitation, suitable patterning and etchingtechniques are used to create the recesses corresponding to one or moreof the second capacitor plates 422 b, 424 b. The result of operation 512is illustrated in FIG. 6E.

At 514, the second capacitor plates 422 b, 424 b, along with additionalconductive and/or metal features to establish electrical communicationbetween the various active, electromechanical, and passive features ofthe RF MEMS device 400 and, optionally, to bond the passive substrate420 to the cap 128, are formed on the interior surface 418 of thepassive substrate 420. For example, the second capacitor plates 422 b,424 b, along with additional conductive and/or metal features, areformed on the interior surface 418 of the passive substrate 420 usingtechniques such as, for example and without limitation suitablepatterning, etching, anodization, and deposition (e.g., chemical vapordeposition and/or physical vapor deposition) techniques. The result ofoperation 514 is illustrated in FIG. 6F.

At 516, the interior surface 130 of the cap 128 is aligned with, imposedon, and bonded to the surface of the active feature layer bearing activefeatures. For example, the recess corresponding to the cavity 126 isaligned with the switch 106, the first capacitor plate 422 a is alignedwith and in electrical communication with the source 102, the secondcapacitor plate 424 a is aligned with and in electrical communicationwith the drain 104, and the gate line 110 is aligned with and inelectrical communication with a conductive contact 117 on the interiorsurface 130 of the cap 128. In one example, the cap 128 and the activefeature layer are bonded using an Au-Au compression bond. In anadditional or alternative example, the cap 128 and the active featurelayer are hermetically bonded. The result of operation 516 isillustrated in FIG. 6G.

At 518, the interior surface 418 of the passive substrate 420 is alignedwith, imposed on, and bonded to the exterior surface 132 of the caplayer 128. For example, the first capacitor plate 422 a and the secondcapacitor plate 422 b are aligned to form the first capacitor 422.Likewise, the first capacitor plate 424 a and the second capacitor plate424 b are aligned to form the second capacitor 424. In one example, thecap 128 and the passive substrate 420 are bonded using an Au-Aucompression bond. In an additional or alternative example, the cap 128and the passive substrate 420 are hermetically bonded. The result ofoperation 518 is illustrated in FIG. 4 . Accordingly, the RF MEMS device400 provides improved electrical, mechanical, and environmentalisolation as well as athermal performance.

In one embodiment, a method includes obtaining an active feature layer.The active feature layer has a first surface bearing one or more activefeature areas and a cap disposed on the active feature layer over theone or more active feature areas. A first electrical connection isformed in electrical communication with a first active feature through afirst contact pad disposed on an interior surface of the cap. A firstcapacitor plate of a first capacitor is formed on an exterior surface ofthe cap in electrical communication with the electrical connection. Afirst bonding pad is formed at a different, spaced-apart location fromthe first capacitor plate on the exterior surface of the cap. A secondcapacitor plate of the first capacitor is formed on an interior surfaceof a passive layer substrate. The passive layer substrate includes atleast one of a silicon-based ceramic, an aluminum-based ceramic, or atantalum-based ceramic. The cap is coupled with the passive layersubstrate so that a first area of the first bonding pad on the capcontacts the second capacitor plate of the first capacitor on thepassive layer substrate and a different, second area of the secondcapacitor plate of the first capacitor overlays and is spaced apart fromthe first capacitor plate of the first capacitor along a direction thatis orthogonal to the exterior surface of the cap to form the firstcapacitor. The cap is bonded with the passive layer substrate.

Optionally, forming includes forming a second electrical connection inelectrical communication with a second active feature through a secondcontact pad disposed on the interior surface of the cap, a firstcapacitor plate of a second capacitor on the exterior surface of the capin electrical communication with the electrical connection, and a secondbonding pad at a different, spaced-apart location from the secondcapacitor plate of the second capacitor on the exterior surface of thecap, wherein the first capacitor plate of the second capacitor and thesecond bonding pad are at a different, spaced-apart location from thefirst capacitor plate and the first bonding pad on the exterior surfaceof the cap. Optionally, forming further includes forming a secondcapacitor plate of the second capacitor on the interior surface of thepassive layer substrate, wherein the second capacitor plate of thesecond capacitor is at different, spaced-apart location from the secondcapacitor plate of the first capacitor on the interior surface of thepassive layer substrate. Optionally, coupling further includes couplingthe cap with the passive layer substrate so that a first area of thesecond bonding pad on the cap contacts the second capacitor plate of thesecond capacitor on the passive layer substrate and a different, secondarea of the second capacitor plate of the second capacitor overlays andis spaced apart from the first capacitor plate of the second capacitoralong a direction that is orthogonal to the exterior surface of the capto form the second capacitor.

Optionally, bonding includes bonding the cap to the passive substrate ata peripheral region using at least one of metal thermocompressionbonding, eutectic bonding, anodic bonding, localized direct laserbonding, or glass frit bonding of the cap to the passive substrate.

Optionally, bonding includes hermetically bonding the cap to the passivesubstrate.

Optionally, the first bonding pad is formed to extend away from theexterior surface of the cap past the first capacitor plate.

Optionally, the method includes forming a recess in the exterior surfaceof the cap and forming the first capacitor plate of the first capacitorformed in the recess.

Optionally, the method includes selecting common height for each of thefirst capacitor plate, the first bonding pad, and the second capacitorplate.

Optionally, the cap includes at least one of a silicon-based ceramic, analuminum-based ceramic, or a tantalum-based ceramic.

Optionally, the at least one of the silicon-based ceramic, analuminum-based ceramic, or a tantalum-based ceramic is formed within thepassive layer substrate.

Optionally, the first electrical connection is a blind via.

Optionally, the electrical communication includes electrical conduction.

Optionally, the method includes forming an electromechanical MEMS devicelayer on one or more portions of the active feature layer.

In one embodiment, a method includes obtaining an active feature layerhaving a first surface bearing one or more active feature areas. A firstcapacitor plate of a first capacitor is formed on an interior surface ofa cap. A second capacitor plate of the first capacitor is formed on anexterior surface of the cap. The first capacitor plate of the firstcapacitor overlays and is spaced apart from the second capacitor plateof the first capacitor along a direction that is orthogonal to theexterior surface of the cap to form the first capacitor. The cap iscoupled with the first surface of the active feature layer such that thesecond capacitor plate of the first capacitor is in electricalcommunication with at least a first active feature of the active featurelayer. The cap is bonded with the passive layer substrate.

Optionally, the forming includes forming a first capacitor plate of asecond capacitor on the interior surface of the cap, wherein the firstcapacitor plate of the second capacitor is at different, spaced-apartlocation from the first capacitor plate of the first capacitor on theinterior surface of the cap; and forming a second capacitor plate of thesecond capacitor on an exterior surface of the cap, wherein the firstcapacitor plate of the second capacitor overlays and is spaced apartfrom the first capacitor plate of the second capacitor along a directionthat is orthogonal to the exterior surface of the cap to form the secondcapacitor. Optionally, coupling includes coupling the cap with the firstsurface of the active feature layer such that the second capacitor plateof the second capacitor is in electrical communication with at least asecond active feature of the active feature layer.

Optionally, the coupling includes positioning the first capacitor withrespect to the first active feature and positioning the second capacitorwith respect to the second active feature such that the capacitorinduces a current in the one or more active features through capacitivecoupling when the capacitor is charged.

Optionally, the method includes forming a recess the interior surface ofthe cap and forming the first capacitor plate of the first capacitor inthe recess.

Optionally, the method includes forming an electromechanical MEMS devicelayer on one or more portions of the active feature layer.

Optionally, the electromechanical device layer includes one or more MEMSswitches.

Optionally, the method includes forming a recess in the interior surfaceof the cap and positioning one or more MEMS switches in the recess.

Optionally, the cap includes at least one of a silicon-based ceramic, analuminum-based ceramic, or a tantalum-based ceramic.

Optionally, bonding includes bonding the cap to the passive substrate ata peripheral region using at least one of metal thermocompressionbonding, eutectic bonding, anodic bonding, localized direct laserbonding, or glass frit bonding of the cap to the active feature layer.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the subject matterset forth herein without departing from its scope. While the dimensionsand types of materials described herein are intended to define theparameters of the disclosed subject matter, they are by no meanslimiting and are example embodiments. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. The scope of the subject matter described herein should,therefore, be determined with reference to the appended claims, alongwith the full scope of equivalents to which such claims are entitled. Inthe appended claims, the terms “including” and “in which” are used asthe plain-English equivalents of the respective terms “comprising” and“wherein.” Moreover, in the following claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to impose numerical requirements on their objects. Further, thelimitations of the following claims are not written inmeans-plus-function format and are not intended to be interpreted basedon 35 U.S.C. § 112(f), unless and until such claim limitations expresslyuse the phrase “means for” followed by a statement of function void offurther structure.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” of the presently describedsubject matter are not intended to be interpreted as excluding theexistence of additional embodiments that also incorporate the recitedfeatures. Moreover, unless explicitly stated to the contrary,embodiments “comprising” or “having” an element or a plurality ofelements having a particular property may include additional suchelements not having that property.

This written description uses examples to disclose several embodimentsof the subject matter set forth herein, including the best mode, andalso to enable a person of ordinary skill in the art to practice theembodiments of disclosed subject matter, including making and using thedevices or systems and performing the methods. The patentable scope ofthe subject matter described herein is defined by the claims, and mayinclude other examples that occur to those of ordinary skill in the art.Such other examples are intended to be within the scope of the claims ifthey have structural elements that do not differ from the literallanguage of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal languages ofthe claims.

Since certain changes may be made in the above-described systems andmethods, without departing from the spirit and scope of the inventivesubject matter herein involved, it is intended that all of the subjectmatter of the above description or shown in the accompanying drawingsshall be interpreted merely as examples illustrating the inventiveconcept herein and shall not be construed as limiting the inventivesubject matter.

Changes can be made in the above constructions without departing fromthe scope of the disclosure, it is intended that all matter contained inthe above description or shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

What is claimed is:
 1. A method, comprising: obtaining an active featurelayer having a first surface bearing one or more active feature areas;forming a first capacitor plate of a first capacitor on an interiorsurface of a cap, wherein the cap includes at least one of asilicon-based ceramic, an aluminum-based ceramic, or a tantalum-basedceramic; forming a second capacitor plate of the first capacitor on anexterior surface of the cap, wherein the first capacitor plate of thefirst capacitor overlays and is spaced apart from the second capacitorplate of the first capacitor along a direction that is orthogonal to theexterior surface of the cap to form the first capacitor; forming a firstcapacitor plate of a second capacitor on the interior surface of thecap, wherein the first capacitor plate of the second capacitor is at adifferent, spaced-apart location from the first capacitor plate of thefirst capacitor on the interior surface of the cap; forming a secondcapacitor plate of the second capacitor on an exterior surface of thecap, wherein the first capacitor plate of the second capacitor overlaysand is spaced apart from the first capacitor plate of the secondcapacitor along a direction that is orthogonal to the exterior surfaceof the cap to form the second capacitor; coupling the cap with the firstsurface of the active feature layer such that the second capacitor plateof the first capacitor is in electrical communication with at least afirst active feature of the active feature layer and such that thesecond capacitor plate of the second capacitor is in electricalcommunication with at least a second active feature of the activefeature layer; and bonding the cap with a passive layer substrate. 2.The method of claim 1, wherein the coupling further comprisespositioning the first capacitor with respect to the first active featureand positioning the second capacitor with respect to the second activefeature such that the capacitor induces a current in the one or moreactive features through capacitive coupling when the capacitor ischarged.
 3. The method of claim 1, further comprising forming a recessthe interior surface of the cap and forming the first capacitor plate ofthe first capacitor in the recess.
 4. The method of claim 1, furthercomprising forming an electromechanical MEMS device layer on one or moreportions of the active feature layer.
 5. The method of claim 4, whereinthe electromechanical MEMS device layer includes one or more MEMSswitches.
 6. The method of claim 5, further comprising forming a recessin the interior surface of the cap and positioning the one or more MEMSswitches in the recess.
 7. The method of claim 5, wherein the one ormore active feature areas include active features and circuitryassociated with MEMS switches.
 8. The method of claim 1, wherein bondingfurther comprises bonding the cap to the passive layer substrate at aperipheral region using at least one of metal thermocompression bonding,eutectic bonding, anodic bonding, localized direct laser bonding, orglass frit bonding of the cap to the active feature layer.
 9. A method,comprising: obtaining an active feature layer having a first surfacebearing one or more active feature areas; forming a first capacitorplate of a first capacitor on an interior surface of a cap, wherein thecap includes at least one of a silicon-based ceramic, an aluminum-basedceramic, or a tantalum-based ceramic; forming a second capacitor plateof the first capacitor on an exterior surface of the cap, wherein thefirst capacitor plate of the first capacitor overlays and is spacedapart from the second capacitor plate of the first capacitor along adirection that is orthogonal to the exterior surface of the cap to formthe first capacitor; coupling the cap with the first surface of theactive feature layer such that the second capacitor plate of the firstcapacitor is in electrical communication with at least a first activefeature of the active feature layer; bonding the cap with a passivelayer substrate; and forming an electromechanical MEMS device layer onone or more portions of the active feature layer.
 10. The method ofclaim 9, further comprising forming a first capacitor plate of a secondcapacitor on the interior surface of the cap, wherein the firstcapacitor plate of the second capacitor is at a different, spaced-apartlocation from the first capacitor plate of the first capacitor on theinterior surface of the cap; and forming a second capacitor plate of thesecond capacitor on an exterior surface of the cap, wherein the firstcapacitor plate of the second capacitor overlays and is spaced apartfrom the first capacitor plate of the second capacitor along a directionthat is orthogonal to the exterior surface of the cap to form the secondcapacitor; and wherein the coupling further comprises coupling the capwith the first surface of the active feature layer such that the secondcapacitor plate of the second capacitor is in electrical communicationwith at least a second active feature of the active feature layer. 11.The method of claim 10, wherein the coupling further comprisespositioning the first capacitor with respect to the first active featureand positioning the second capacitor with respect to the second activefeature such that the capacitor induces a current in the one or moreactive features through capacitive coupling when the capacitor ischarged.
 12. The method of claim 9, further comprising forming a recessthe interior surface of the cap and forming the first capacitor plate ofthe first capacitor in the recess.
 13. The method of claim 9, whereinthe electromechanical MEMS device layer includes one or more MEMSswitches.
 14. The method of claim 13, further comprising forming arecess in the interior surface of the cap and positioning the one ormore MEMS switches in the recess.
 15. The method of claim 13, whereinthe one or more active feature areas include active features andcircuitry associated with MEMS switches.
 16. The method of claim 9,wherein bonding further comprises bonding the cap to the passive layersubstrate at a peripheral region using at least one of metalthermocompression bonding, eutectic bonding, anodic bonding, localizeddirect laser bonding, or glass frit bonding of the cap to the activefeature layer.
 17. A method, comprising: obtaining an active featurelayer having a first surface bearing one or more active feature areas;forming a first capacitor plate of a first capacitor on an interiorsurface of a cap, wherein the cap includes at least one of asilicon-based ceramic, an aluminum-based ceramic, or a tantalum-basedceramic; forming a second capacitor plate of the first capacitor on anexterior surface of the cap, wherein the first capacitor plate of thefirst capacitor overlays and is spaced apart from the second capacitorplate of the first capacitor along a direction that is orthogonal to theexterior surface of the cap to form the first capacitor; coupling thecap with the first surface of the active feature layer such that thesecond capacitor plate of the first capacitor is in electricalcommunication with at least a first active feature of the active featurelayer; and bonding the cap with a passive layer substrate at aperipheral region using at least one of metal thermocompression bonding,eutectic bonding, anodic bonding, localized direct laser bonding, orglass frit bonding of the cap to the active feature layer.
 18. Themethod of claim 17, further comprising forming a first capacitor plateof a second capacitor on the interior surface of the cap, wherein thefirst capacitor plate of the second capacitor is at a different,spaced-apart location from the first capacitor plate of the firstcapacitor on the interior surface of the cap; and forming a secondcapacitor plate of the second capacitor on an exterior surface of thecap, wherein the first capacitor plate of the second capacitor overlaysand is spaced apart from the first capacitor plate of the secondcapacitor along a direction that is orthogonal to the exterior surfaceof the cap to form the second capacitor; and wherein the couplingfurther comprises coupling the cap with the first surface of the activefeature layer such that the second capacitor plate of the secondcapacitor is in electrical communication with at least a second activefeature of the active feature layer.
 19. The method of claim 18, whereinthe coupling further comprises positioning the first capacitor withrespect to the first active feature and positioning the second capacitorwith respect to the second active feature such that the capacitorinduces a current in the one or more active features through capacitivecoupling when the capacitor is charged.
 20. The method of claim 17,further comprising forming a recess the interior surface of the cap andforming the first capacitor plate of the first capacitor in the recess.